Abstract
Recording and analysis of normal patterns of growth and development of the human face are among the most important clinical observations. Three-dimensional digitization technologies can now record three-dimensional coordinates of facial surfaces, allowing direct analyses of landmark coordinates that provide the basis for statistical differences in facial shape during growth and development. The aim of this study was to compare methodologies used to establish the three-dimensional coordinate system for quantifying facial morphology.The three-dimensional facial morphology of infants was recorded using a three-dimensional laser surface scanner system (VIVID 910, KONICA MINOLTA SENCING, Inc. Osaka, Japan). One hun dred and twenty normal developing children (20 boys and 20 girls each at 4, 5 and 6 years of age) had their faces scanned by VIVID.Two origins and two reference planes for the scanned data were established and compared to evaluate the effectiveness and importance of the selected coordinate system. The first origin was at Nasion on the soft tissue, and the second was defined as the mid-point of both the right and left Endocanthion points. The first reference plane was a Nasal triangle based on three reference markers : soft tissue Nasion in the midline and Alar crests on each side. The second plane was based on 8 points,Exocanthion, Endocanthion, Alar crest and Cheilion on both right and left sides. The vertical axis was defined using 6 points : G, S, Prn, Ls, Li and Pog. The lateral axis was perpendicular to the vertical axis on the established plane, and the anterior-posterior axis had the same direction as the unit vector of the plane.The Endocanthion mid-point was the better origin, resulting in slightly smaller standard deviations and coefficients of variance of all measurements, especially on the vertical axis and three-dimensional distances. When the two reference planes were compared using this origin they differed for measurements in the sagittal plane by an average of 9.7 degrees. This angle decreased with growth, and a statistically significant difference was found between 4- and 6-year-old girls. No significant differences were detected on the horizontal plane.These results suggest that the selection of the coordinate system can influence observed measurements of growth, development and even treatment effects of the face. Therefore, the coordinate system should be chosen based on the purpose of the study and the characteristics of each landmark.
